No, 'A Ghost in Monte Carlo' isn't based on actual historical events; it's a work of fiction, specifically a romantic novel by Barbara Cartland. The core story—a young woman disguising herself, becoming entangled with a mysterious man, and navigating high society—is pure melodrama crafted for entertainment. You can find parallels to true events in a very general sense, like the real opulence of Monte Carlo in the late 19th century or the social constraints on women, but the specific plot is invented.
That said, the atmosphere feels authentic because Cartland did her research on the setting. The glamour, the casinos, the costumes—it all grounds the fantastical plot in a recognizable historical backdrop. It's the kind of story that plays with the idea of truth, using a real, glittering location to make its romantic escapism more convincing. So while the ghost and the intrigue aren't real, the world it's set in certainly was.